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Oct 03, 2020, 03:09 PM
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Build Log

GMP Cricket Conversion to Electric Power


I learned to fly helis on a GMP Cricket back in 1980. It was a great little heli that was able to take a LOT of abuse! A few years back I came across a Cricket kit here in the RCG Classifieds and, on a whim, I purchased it!

I had planned on building it as a glow model, but the more I fly my electric stuff, the less interest I have in flying anything glow powered. I considered selling the kit, but then it hit me.....why not try an e-power conversion? So that's what I've decided to do.

The kit seems to be complete right down to all the paperwork. In the enclosed pamphlet there were even a couple photos of a two very familiar clowns as seen in the last photo below!

This will be a relatively slow build for a heli since I have to make a lot of the parts for the conversion plus I plan to incorporate all the little tricks that we learned back in the day to make the Cricket fly as well as it can.

Ralph
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Oct 03, 2020, 03:16 PM
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Besides the kit I have a few Cricket parts & pieces in my stash that I can draw from if need be. I will most likely use the frame assembly shown in these photos instead of the one in the kit just because I like the black anodizing.

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Oct 03, 2020, 03:28 PM
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The first order of business was to find a motor. I picked up this 500 class 1300KV motor from Altitude hobbies. I'm planning on using a 4S 3500 mAh battery. With 1300KV, 4S should give me the performance I'm looking for. If not the motor can handle up to 7S if need be, but I doubt I'll have to go there.

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Oct 03, 2020, 03:44 PM
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I've seen a few videos online of Crickets that have been converted to e-power and they have all used the stock flywheel/clutch assembly attached to the motor. I don't think a clutch is necessary on an electric heli and I plan to go direct drive, more or less!

I found the proper 11T drive pulley at Stock Drive Products. I also picked up a 3/8" wide polyurethane drive belt. This belt is reinforced with Kevlar cords. Even though this belt is 1/8" wider than the stock neoprene 1/4" belt it is also considerably more flexible and much stronger. I'm hoping it has less drag than the stock belt due to it's flexability.

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Oct 03, 2020, 03:53 PM
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The first machining task was to figure out a way to attach the 11T pulley to the motor at the proper location. After some head scratching and a lot of measuring I came up with this setup.

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Oct 03, 2020, 03:56 PM
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Up next was the motor bracket. It's made from 3/16", 6061-T6 aluminum plate.

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Oct 03, 2020, 04:00 PM
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Then came the pulley support bracket. The bearing is the same 6mm I.D. bearing used on the clutch shafts on GMP Competitors, Cobras and Legends.

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Oct 03, 2020, 04:04 PM
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The next step was to come up with a motor plate to hold all this stuff together. I mocked one up with 1/8" light ply first before I started to cut metal.

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Oct 03, 2020, 04:07 PM
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The completed motor plate made from 1/8", 6061-T6 aluminum.

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Oct 03, 2020, 04:14 PM
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And finally the completed motor plate assembly. The next step is to get this unit mounted to the main frame. I hope to get that accomplished sometime this weekend or next.

So far I'm pretty happy with how this is working out. I'm looking forward to finishing this project and flying a Cricket again! Without the oily mess!

Ralph
Oct 03, 2020, 05:49 PM
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This is REALLY interesting!

I have one Cricket, ready to go (still nitro) but have not flown it in years. These were/are wonderful little machines!

Please keep posting your photos sir! Your machine work is beautiful!
Oct 04, 2020, 10:31 AM
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Thanks for the kind words!

I'm making CAD drawings of all the parts that I make for this conversion. In the end, if it works out as well as I hope it will, I'll make those drawings available to anyone that would like to convert their own Cricket to e-power. I'm sure there are literally thousands of people out there that are just dying to fly an electric Cricket!

Ralph
Oct 04, 2020, 12:07 PM
Is what I'm doing helping?
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Flawless machining, they look like factory parts.

Had bunches of nitro powered cars and trucks when I was younger, but back then
I had the energy to clean up the mess.

One time my wife came home and I was washing my T-Maxx in the bathtub.
She was really mad but then I gave her money to go shopping. These R/C hobbies can get expensive.

I looked at the exploded view and noticed it was fixed pitch, and watched a few videos.
The electric conversion should make it easier to fly, since you will have more precise throttle control with instant response.
Last edited by Steve_; Oct 04, 2020 at 01:15 PM.
Oct 04, 2020, 03:08 PM
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Thanks Steve!

Yeah, I think better throttle response and probably more motor torque will make a big difference in flight performance!

One thing I noticed on most of the Cricket videos that I've seen is that the rotor speeds are much too slow which makes control response sluggish. Most likely they're running too much pitch. The Cricket needs to windup pretty high to really preform well.

Ralph
Oct 04, 2020, 03:16 PM
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I had some time today and was able to attach the power unit to the main frame.

I was a little concerned about getting the alignment just right and having the belt run to one extreme or the other. But, just rotating the motor by hand it appears the alignment is fine. The belt pretty much runs in one spot no matter which direction the motor is rotated. I guess I got lucky!

Looks like it's time to order an ESC and a battery so I can spin this thing up!

Ralph


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